1. Field of the Invention
The present invention relates to a code detection apparatus, which detects spectrum-spread codes contained in a pilot signal to be transmitted by a base station in each cellular zone in a code division multiple access (CDMA) cellular type communication system and communication systems equivalent to this.
2. Description of the Related Art
In the CDMA cellular type communication system, a pilot signal (pilot channel) modulated by a spectrum-spread code (PN code) is constantly transmitted from a base station in a cellular zone. Such pilot signal is used for detecting and maintaining the synchronization at a mobile unit(s). As the pilot signal, two types of PN codes pn.sub.i and pn.sub.q of the same cycles and different pseudo random number sequences are used.
However, when establishing synchronization between a base station and a mobile unit, at the initial stage thereof, there are cases where the transmission carrier signal frequency .omega..sub.1 on the base station side and the reception carrier frequency .omega..sub.2 on the mobile unit side deviate from each other. In such a case, the error in the calculations for the synchronization processing becomes larger and the detection of synchronization and the holding thereof sometimes cannot be carried out well.